Does it matter?
light contact, just let them nestle in slight effort required. It does matter, because your upper teeth will have a greater distance apart than your lower teeth which will result in complications later on.
Together. You do not want your face to lengthen, Keeping the teeth together makes sure the lower jaw expands in contination with the upper jaw.
Where ever your tongue places them. Keeping your teeth together or slightly apart should not require any effort. All the work is done by the tongue. When you posture your tongue on the roof of your mouth and engage suction the mastication muscles will engage by retracting the mandible upward and forward. The effect is either lightly closed teeth or almost.
my story: http://www.aljabri.com/blog/my-story/